The interaction between aerobic exercise and drug abuse is relatively unexplored. It deserves attention because recent data suggest neuroadaptations from exercise promote learning in circuits that overlap with drug abuse. The hippocampus is an important point of intersection because it is a major locus for change from aerobic exercise and it plays a central role in contextual conditioning. Specifically, contextual cues paired with drugs trigger emotional responses related to craving and relapse. The long-term goal of this research program is to identify molecular and physiological mechanisms underlying the influence of exercise on drug-related behaviors in mice. The overall objective of this application is to develop a mouse model to study the effects of wheel running exercise on extinction of cocaine conditioned place preference, and to test one hypothesized mechanism for how exercise can influence Pavlovian drug associations. The central hypothesis is that new neurons from exercise can cause drug associations to persist if the drug is administered at a critical period in the development of the new neurons when they are preferentially recruited into learning networks. This is supported by the Preliminary Studies that show resistance to extinction of conditioned place preference for cocaine in runners as compared to sedentary animals after re-exposure to cocaine in context. The objective of this application will be accomplished by pursuing two specific aims. Aim 1 is to identify the impact of aerobic exercise on extinction of conditioned place preference for cocaine. Based on Preliminary Studies, the working hypothesis is that exercise will either facilitate or delay extinction of conditioned place preference depending on whether drug exposure occurs before or after exercise training, in parallel with increased adult hippocampal neurogenesis in the dentate gyrus. To accomplish this aim, the order of conditioning and exercise treatments will be manipulated, and then conditioned place preference will be measured repeatedly until extinction. Animals will be injected with BrdU to label dividing cells, and the number of BrdU cells co-labeled with neuronal nuclear marker, NeuN, in the granule layer of the dentate gyrus will be used to measure neurogenesis. Aim 2 is to determine the extent to which new neurons from exercise causally contribute to persistence of conditioned place preference for cocaine. Based on Preliminary Studies, the working hypothesis is that new neurons from exercise will function to enhance Pavlovian conditioning. This hypothesis will be directly tested by reducing neurogenesis using 2 separate methods, a transgenic mouse model and focal gamma irradiation, to determine whether new neurons are required for exercise to delay extinction of place preference. The extent to which new neurons are preferentially recruited into circuits involved in cocaine conditioning will also be determined by measuring the proportion of BrdU positive versus negative cells expressing c-Fos in response to the preference test. The project will discover mechanisms for interactions between exercise and drug abuse. This will be useful for evaluating the benefits or risks of incorporating exercise in treatment of drug abuse.

Public Health Relevance

This proposal will discover the impact of enhanced neuroplasticity from aerobic exercise on extinction of cocaine conditioned behavior in a mouse model. The project will provide useful evidence for evaluating the benefits or risks of incorporating exercise in treatment of drug abuse.